This proposal outlines a comprehensive career development plan for the PI consisting of advanced coursework and hands-on laboratory based training in immunology, multidisciplinary mentoring, and practical experience via the completion of the proposed research project. With the K23 Career Development Award, Dr. Kelley will develop the skills necessary to attain her goal of an independently funded HIV translational research career with a focus on biomedical HIV prevention interventions and HIV transmission. Dr. Kelley's ultimate goal is to one day make important contributions to the science of HIV prevention, including optimizing biomedical prevention interventions and vaccine development, for populations at high risk of infection. In order to attain her training goals, Dr. Kelley will b co-mentored during the K23 award period by an immunologist and HIV vaccinologist, Dr. Rama Amara, and an epidemiologist with expertise in HIV prevention for MSM, Dr. Patrick Sullivan. She will emerge from this award period skilled in mucosal immunology, which in combination with her previous extensive experience in clinical HIV medicine, epidemiology, and clinical/translational research, will position Dr. Kelley well to pursue an independently funded research career and one day be a leader in the field of biomedical HIV prevention interventions. Men who have sex with men (MSM) continue to have the highest risk for HIV infection in the US, accounting for 63% of new infections in 2010, underscoring the urgent need for effective prevention interventions in this population. Recent advances in biomedical prevention strategies including pre-exposure prophylaxis (PrEP), vaccines, and microbicides, have energized the field around further development and implementation of these interventions for key populations at higher risk. However, one potential barrier to the effectiveness of these interventions in MSM is the relative ease of HIV transmission across the rectal mucosa, where approximately 70% of infections occur among MSM, as compared to vaginal or penile transmission. In addition, very little is known about how unprotected receptive anal intercourse (URAI) may modify the rectal mucosa and mucosal HIV target cell populations. We hypothesize that sexually active HIV-negative MSM at risk for HIV infection who engage in URAI will have evidence of (1) reduced mucosal integrity, (2) more mucosal inflammation, and (3) greater HIV target cell availability in the rectal mucosa as compared to men who do not engage in anal intercourse. To test these hypotheses, MSM who engage in URAI and controls will be recruited into a longitudinal study with peripheral blood and rectal mucosal biopsy sampling. First, in a cross-sectional study, we will explore global gene expression differences between MSM and controls in the rectal mucosa with particular attention to gene expression of the epithelial cell junction complex, pro-inflammatory cytokines, and cell proliferation/apoptosis pathways. Next, based on the gene expression analyses, we will choose differentially expressed biomarkers and examine longitudinal differences between MSM and controls in the rectal mucosa epithelial cell layer with quantitative immunohistochemistry. Finally, differences in the CD4+ and CD8+ T cell populations in the rectal mucosa with respect to expression of the HIV co-receptor, CCR5, memory phenotypes, and activation status will be examined for MSM and controls. Advancing knowledge of how URAI affects the rectal mucosa will provide critical information in two areas. First, it may help to elucidate the differential efficacy of current and future biomedical preventin interventions specifically for MSM populations at high risk. Second, it may suggest other adjunctive therapies to improve efficacy of biomedical prevention interventions. For example, if MSM who engage in URAI exhibit greater inflammation and/or reduced rectal mucosal integrity, an adjunctive therapy that targets these abnormalities used in conjunction with other biomedical prevention interventions could improve their efficacy. RELEVANCE: Men who have sex with men (MSM) continue to be disproportionately affected by HIV. This study will examine differences in mucosal integrity, inflammation, and cell populations in the rectal mucosa between HIV negative MSM who engage in unprotected receptive anal intercourse and men who do not engage in anal intercourse. Differences seen in these mucosal parameters may identify new targets for intervention and could lead to improvements in efficacy of current and future biomedical HIV prevention interventions.